Preheat oven to 400 degrees F (200 degrees C). Lightly brush the cut sides of the butternut squash halves with olive oil, then place them cut-side down on a baking sheet. Roast for 40 to 45 minutes until completely tender when pierced with a fork. Remove from oven, let cool slightly, then scoop out the flesh and mash lightly with a fork.

While the squash roasts, bring a large pot of salted water to a boil. Cook pasta according to package directions until just al dente. Reserve 1 cup of pasta water before draining. Drain and set aside.

Heat 1 tablespoon olive oil in a large skillet over medium heat. Add the Italian sausage and cook for 5 to 7 minutes, breaking it up with a wooden spoon until evenly browned throughout.

Add the diced onion and minced garlic to the skillet. Cook over medium heat for 3 to 4 minutes, stirring occasionally, until softened and fragrant. Keep the heat at medium to prevent the garlic from burning.

Stir in the dried sage, thyme, and red pepper flakes. Let the spices bloom for about 30 seconds.

Pour in the chicken broth and simmer for 5 minutes, scraping up any browned bits from the bottom of the pan.

Add the heavy cream gradually while stirring, then add the freshly grated Parmesan cheese. Stir continuously until the cheese is fully melted and the sauce has thickened, about 2 to 3 minutes.

Fold in the roasted butternut squash and cooked pasta, tossing gently to coat everything in the sauce. Add a splash of reserved pasta water if the sauce needs loosening. Season generously with salt and pepper. Heat through for 2 to 3 minutes.

Let the dish rest for 1 minute before serving to allow the flavors to meld. Divide into bowls and garnish generously with fresh parsley.